Answer:
B
Explanation:
Option B is the correct answer. When you add 7 in front of the O2 in the left side, and then you add 4 and 6 in front of NO2 and H2O respectively, the number of oxygen atoms is the same in both sides.
I believe it is 3 and 4. I really hope it is but i am positive :)
The difference between all of them in the make-up of the R group.
